Stem cells today constitute a valuable therapeutic potential, in particular from the point of view of regenerative or therapeutic medicine. They group together various specific cell categories:                adult stem cells: the first discovered were blood cells. They are widely used after chemotherapy, which destroys the bone marrow cells. An autologous graft (from the patient himself) makes it possible to produce blood cells more rapidly, without the risk of rejection. All tissues and all organs contain adult stem cells, but they are rare and difficult to purify;        perinatal stem cells: they are contained in the umbilical cord, the placenta and the blood which is contained therein. Mention may be made of blood stem cells, which can be used for grafts, but must be compatible from an immunological point of view;        mesenchymal stem cells: they can be both perinatal (contained in the umbilical cord and the placenta) and adult. They then originate mainly from the bone marrow and the adipose tissue;        embryonic stem cells: these cells originate from “surplus” embryos, and are particularly advantageous for research since they are completely undifferentiated and can become specialized for all the human tissues. There are of course medical applications (compensating for the deficiencies of certain organs), but also pharmacological applications; and finally        reprogrammed cells, also called “induced pluripotent stem cells” or “iPS” cells: by introducing 4 genes capable of completely reprogramming it, researchers have transformed a differentiated adult skin cell into a pluripotent stem cell. This technique has been used on mice suffering from sickle-cell anemia. The diseased red blood cells were corrected by gene therapy, dedifferentiated, and then reinjected into the mouse. A cure could thus be obtained using cells from the sick mouse itself.        
In order to be able to use these stem cells in therapy and to develop applications thereof, it is necessary to preserve them, for the desired time, in the undifferentiated state. This is because said cells differentiate very rapidly into a given cell type, which makes them unusable for (re)directing their differentiation toward a different cell type, or for carrying out fundamental research studies on these cells.
There is therefore a need to maintain stem cells, in particular animal stem cells, more particularly human stem cells, in the undifferentiated state in order to trigger the differentiation process at the desired moment.
The inventors have now discovered that, surprisingly, the extracellular hemoglobin from annelids, when it is added to stem cells, in particular human stem cells, makes it possible to maintain the latter in the undifferentiated state, while at the same time preserving their viability.